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When my AprilAire 768 was reinstalled on my new Trane variable speed gas furnace last year, it was configured to run any time the fan is running (pickup on fan wire senses current and turns on humidifier if it's calling for humidification). Since the fan runs at a very slow speed 24/7 (at the installer’s recommendation), the humidifier runs even when the furnace isn’t heating. It does use hot water so I imagine it would humidify some, but does that make any sense?

The 768's solonoid has failed so I'm getting ready to replace it with a new model 700 w/ outdoor temp sensor. I'm wondering if I should use HUM terminal from the furnace instead of running it based on the fan operation.

If I use the HUM terminal (wire goes from board to junction box), can I connect that directly to the power wire from the humidifier control? What should I hook the common to (there's a common HUM terminal, but no jumper wire to junction box)? Is the neutral in the junction box OK?